Toolboard failures

DuetUser

We have a long story of failed toolboards.
5 pieces of 1.2A version with different errors like wrong temperature readout, unable to connect or not extruding.
1.3 are much better, but today the second one went bust out of the blue with :
"Error: Expansion board 121 stopped sending status"

I'm not here to complain or rant,
although I hate them with passion due to microscopic connectors and cables in all directions :).
We definitely will be using them forever as they reduce cable mileage.

The question is are there any safety concerns while connecting them, maybe there is a surge from 3m PTFE tubing or something alike. I assume they operate in suboptimal conditions which cause problems.
I just don't know what can be possible errors with mounting/wiring ?

droftarts

@DuetUser Wrong temperature readout would imply that something has zapped the MCU or associated temperature reading circuit, and the most likely culprit is static electricity. Failures like this generally occur during printing. We recommend grounding the extruder and motor. See https://docs.duet3d.com/en/User_manual/Connecting_hardware/Power_wiring#grounding
The Roto and 1LC toolboards can be grounded conveniently:

On Duet toolboards (Roto, 1LC v1.3 and later) the mounting screw holes are all grounded to VIN negative via 100K resistors to provide a path to ground for any static build up.

Grounding is also mention here: https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Toolboard_1LC#wiring-notes

We recommend connecting the hot end metalwork to ground on the toolboard via a resistor (10k to 1M Ohm), if it is not grounded through its mounting system. This will prevent the hot end building up static charge, which might otherwise occur as filament is extruded and may then flash over to the tool board thermistor input, causing damage.

A big enough static discharge will completely kill the MCU.

For the ones that are not extruding, it may be they are running older versions of the firmware compared to the main board, ie toolboard on 3.4, while the mainboard is on 3.5. This usually stops extrusion, while everything else looks okay.

It may also be worth updating toolboards to the latest bootloader, see https://docs.duet3d.com/en/User_manual/RepRapFirmware/Updating_bootloader

Ian